We always hear stupid batman stories where he tells someone whose about to cross the line "if you kill (whatever villian) I will hunt you down and bring you to justice". When you think about it thats one of the most empty threats possible. You could probably kill joker in broad daylight ala (kingdom come) and get off scott free. You could argue Joker poses a real and consitant threat since he keeps escaping arkham . The recent villian "nobody" could have murdered almost all of batmans rogue gallery and walked into the police station and confessed and I doubt would get any time.
Which brings me to another point. Joker has filled a graveyard with dead bodies. You mean to tell me none of those families decided they wanted revenge? Deathstrokes the most obvious assassin that could get it done without a problem. Shiva too.
Eh, the majority of people Joker has killed wouldn''t have families rich enough to hire the A-list assassins. There's also the fact that pretty much no supervillain wants to act against the Joker because most of them are terrified by him.
But those are just in universe ways of explaining plot armour tbh.
Its hard to take that serious some times. Dont get me wrong I love the Joker character but there are plenty of sociopaths in DC that the whole crazy schick wont fly with. Hell I remember Bane treated him like a ***** in NML and people like deathstroke, mr freeze, poison ivy are each more than capable (and willing) of killing him.
Joker probably has thousands of victims with families in all walks of life. It would work like a class action, they all put in whatever they can afford, a few hundred, a few thousand, twenty thousand, fifty thousand... pretty soon it all adds up and they can hire Deathstroke to do the job nice and professional.
That was the opening scene in Kevin Smith's Batman: Cacophony. Deadshot - not Deathstroke - had been hired by a rich family to break into Arkham and kill the Joker, due to the family's young son being killed by a party drug offshoot of Joker Venom called 'Chuckles.' He was nearly ready to do it when Onomatopoeia breaks in and kidnaps Joker for his own plan.
It's the unspoken truth about the Batman stories; that some bystander could gun Joker down in broad daylight, and despite being arrested and James Gordon getting in a tizzy about the necessity of the law, no jury would convict this person when it came time for trial. It's a problem DC created for themselves when they decided to let the character get murderous again after The Dark Knight Returns in the mid 1980's, and it's gotten worse & worse. Hell, Batman has gotten a second villain in that time in Szasz who's a straight up serial killing sicko, and all he does is get sent to Arkham again & again.
Batman, unfortunately, is equated with being the equal of the law & order departments in Gotham City - Spider Man and Daredevil don't have that kind of pressure as vigilantes. The failure of the system is his failure, too. He can say he doesn't have the right to make martial decisions about the worst criminals in the city...but for him and the Gotham police, the argument has looked increasingly hollow; for decades now.
"Everyone else may be an a**hole, but I'm not!" - Harlan Ellison
If Batman killed the Joker tomorrow, he'd be seen as a hero who murders his villains, and while some would sympathise with him, Batman's mental state is going to be called in to question, and the League would hunt him.
Yeah but that's kinda forgetting the fact Joker is nearly as hard to get a jump on as Batman, it's not like he's going to sit around and wait for Deathstroke to kill him. I mean, sure in a straight up fight Joker would get killed, but the fact is he's incredibly smart and well prepared, and would almost certainly hear about it if Deathstroke was gunning for him.
If he only killed Joker, the League would be concerned and talk with him but I doubt they'd hunt him down and make him stop being a hero. I'm sure they'd understand since many of them have killed someone before.
Then they'll make him retire, and stop him forcefully if they need to. I'd just like to think they'd be disappointed and worried but understanding if one day he got pushed to fire and killed a villain.